EP1861957B1 - Verfahren und system zur bekanntgabe von zugangspunkt-kandidaten in einem drahtlosen netzwerk - Google Patents

Verfahren und system zur bekanntgabe von zugangspunkt-kandidaten in einem drahtlosen netzwerk Download PDF

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Publication number
EP1861957B1
EP1861957B1 EP06711071A EP06711071A EP1861957B1 EP 1861957 B1 EP1861957 B1 EP 1861957B1 EP 06711071 A EP06711071 A EP 06711071A EP 06711071 A EP06711071 A EP 06711071A EP 1861957 B1 EP1861957 B1 EP 1861957B1
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Prior art keywords
access point
channel
station
announcement frame
transmitting
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French (fr)
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EP1861957A1 (de
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Amjad Soomro
Dave Cavalcanti
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Koninklijke Philips NV
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Koninklijke Philips Electronics NV
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    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04WWIRELESS COMMUNICATION NETWORKS
    • H04W48/00Access restriction; Network selection; Access point selection
    • H04W48/08Access restriction or access information delivery, e.g. discovery data delivery
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04WWIRELESS COMMUNICATION NETWORKS
    • H04W24/00Supervisory, monitoring or testing arrangements
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04WWIRELESS COMMUNICATION NETWORKS
    • H04W36/00Hand-off or reselection arrangements
    • H04W36/0005Control or signalling for completing the hand-off
    • H04W36/0055Transmission or use of information for re-establishing the radio link
    • H04W36/0072Transmission or use of information for re-establishing the radio link of resource information of target access point
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04WWIRELESS COMMUNICATION NETWORKS
    • H04W88/00Devices specially adapted for wireless communication networks, e.g. terminals, base stations or access point devices
    • H04W88/08Access point devices

Definitions

  • the invention relates to a method and system for identifying candidate access points in a wireless network.
  • the IEEE 802.11 standard specifies the medium access control (MAC) and physical layer characteristics for a wireless local area network (WLAN).
  • the IEEE 802.11 standard is defined in International Standard ISO/IEC 8802-11, "IEEE Standard for Information technology-Telecommunications and information exchange between systems-Local and metropolitan area networks-Specific requirements, Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications," 1999 Edition [1].
  • Supplements to 802.11 comprise: IEEE 802.11h, IEEE TGk draft D 0.14, and IEEE TGe draft D8.0.
  • Roaming occurs when a mobile station (STA) moves from the coverage area from one access point (AP) to another AP. Before a STA could begin exchanging data with the new AP, a STA, typically: 1) scans for and discovers potential AP/APs to which it can roam; 2) decides on the target AP to which it should roam; and 3) executes association, authentication, and resource allocation protocols, if any. Part of the roaming delay is due to the scan process, in which the mobile stations (STAs) try to find an access point (AP) candidate to start an association/reassociation procedure. STAs can discover candidate APs for roaming by detecting beacons and via probe requests and responses.
  • US 2004/0039817 A1 describes a wireless network in which a wireless station selects an access point, e.g., during power-up or roaming, based on the received signal strength indicator (RSSI) and channel loading information. This selection involves checking all frequencies.
  • RSSI received signal strength indicator
  • IEEE 802.11, including TGk provides for WLAN roaming capability.
  • This specification provides for scanning for channels in a certain range that are permitted.
  • a wireless station receives reports such as a Site Report or Neighbor Report collected from the APs that says which channels are available in the station's neighborhood. This reduces the amount of scanning required to determine available channels and minimizes a lag in transmission time.
  • APs can also transmit information about available channels and other APs in the neighborhood in the form of periodic beacons, in response to measurement requests or autonomously. When a STA receives such information it knows of the existence of neighbor APs.
  • Prior art roaming involves STA switching to an operating channel of an AP in the received neighbor list and determining the signal level from that AP. Therefore, even with a list of valid channels and/or neighbor APs, the STA may still have to choose between several candidates to start the roaming process. Further, if the STA selects a candidate AP outside its communication range, then the STA will have to try another candidate AP, which will increase the discovery delay. Additionally if the candidate AP is in the opposite direction to the STA's current direction of movement this will increase the delay. Also, if the STA chooses a candidate AP with a high traffic load, it may experience more delay because the AP may not be able to support a required service level.
  • a list of neighbor APs and/or channels may not always guarantee a small scan delay.
  • a STA wastes time and energy trying to send a probe to an AP that is not within its coverage or may be overloaded due to the lack of information provided in the neighbor reports and channel lists.
  • the invention allows an AP to transmit frames announcing its capabilities in a channel where it is not serving. For example, if an AP is operating in channel 1 and has created a Basic Service Set ID (BSSID) in that channel, it is permitted to transmit frames announcing its capabilities in another channel, for example channel 3, where another AP may or may not be operating.
  • BSSID Basic Service Set ID
  • the invention enables an STA to identify which AP is within its coverage, the received signal strength from the APs, as well as resource availability in each AP.
  • the invention enables a STA to determine the best AP to roam to in less time by avoiding attempts to scan or associate with APs that cannot support its service requirements or which are not reachable.
  • FIG. 1 illustrates a wireless LAN (WLAN) 20 system for implementing the method of the invention.
  • Wireless LAN 20 defines an infrastructure network which includes a plurality of cells 22.
  • Cell 22 includes an access point (AP) 24 (which is sometimes referred to as a wireless local bridge or a base station).
  • AP access point
  • cell 22 may include remote network stations (STAs) 26.
  • STAs remote network stations
  • Access point 24 and remote STAs 26 may be the transmitters and receivers of the system.
  • Each STA 26 may be a mobile, portable, or stationary terminal.
  • Each STA 26 may be a desktop workstation, laptop computer, palm top computer, handheld personal computer, pen-based computer, personal digital assistant, handheld scanner, data collector, handheld printer, etc.
  • AP 24 may be an interface for communicating between wireless network 20 and a wireline network.
  • AP 24 may be configured to provide a communications gateway between STAs 26 and AP 24 that are in cell 22 and also between a wireline network and the STAs 26.
  • AP 24 is typically configured to convert signals between wireline and wireless communications mediums. The conversion may allow the access point to pass communication information between the wireline network and wireless STAs 26.
  • the wireline network may be coupled to an external network 29 (e.g., PBX, PSTN, Internet, etc.).
  • AP 24' and AP 24" are additional APs with additional coverage areas to which STAs 26 can roam.
  • both an AP and a STA may include a display 30, a CPU 32, a transmitter/receiver 34, an input device 36, a storage module 38, a random access memory (RAM) 40, a read-only memory 42, and a common bus 41.
  • RAM random access memory
  • the transmitter/receiver 34 is coupled to an antenna (not shown) to transmit desired data and its receiver converts received signals into corresponding digital data.
  • the CPU 32 operates under the control of an operating system contained in the ROM 42 and utilizes RAM 40 to perform the frequency selection within a wireless local area network (WLAN), by enabling the AP in an infrastructure network or a STA in an ad-hoc network, to provide a new channel or wireless link for the rest of stations (STAs).
  • WLAN wireless local area network
  • a plurality of STAs 26 may be associated with AP 24 if present. Each STA 26 may have different communications capabilities and requirements.
  • AP 24 may manage the communications traffic between STAs 26 and the wireline network. AP 24 may manage the communications traffic by controlling when frames are transmitted to each remote STA 26 in cell 22.
  • the communications traffic in cell 22 may include data frames (e.g., signals that carry frames to provide data communications), voice frames (e.g., signals that carry frames to provide voice communications), real-time frames (e.g., signals that carry frames to provide real-time communications such as multimedia or voice communications), management frames (e.g., signals that carry frames to provide network management communications), etc.
  • data frames e.g., signals that carry frames to provide data communications
  • voice frames e.g., signals that carry frames to provide voice communications
  • real-time frames e.g., signals that carry frames to provide real-time communications such as multimedia or voice communications
  • management frames e.g., signals that carry frames to provide network management communications
  • AP 24 may broadcast or transmit an AP announcement frame 50 (shown in Fig. 3 ). Regulatory domain information may be included in and conveyed with the report in a serving channel of an AP, or in a non-serving channel of a different AP.
  • Fig. 3 depicts an AP announcement frame 50 that contains pertinent information on a collection of APs that are candidates to which STAs can roam.
  • a STA may determine the best AP to roam to in less time by allowing an AP to transmit frames announcing its capabilities in a channel where it is not serving (e.g., a non-serving channel).
  • An AP announcement frame 50 as depicted in Fig. 3 provides this information.
  • An AP sends this AP announcement frame 50 in non-serving channels being used by other neighboring APs.
  • the AP announcement frame 50 contains the AP's serving channel, information about the AP's capabilities, and resource availability.
  • the AP announcement frames provide information for STAs to decide the best AP candidate for roaming.
  • AP announcement frame 50 can carry any measurement information, such as neighbor reports or channel load report.
  • AP announcement frame 50 could be autonomously sent by APs (e.g., as a Class 1 frame carrying the same information or part of the information included in the beacon frames) or sent upon request of other STAs.
  • the AP announcement frame 50 contains several fields 51-57, some of which will be discussed.
  • the BSSID field 51 is a 48-bit field of the same format as an IEEE 802 MAC address. This field uniquely identifies each BSS. The value of this field, in an infrastructure BSS, is the MAC address currently in use by the STA in the AP of the BSS.
  • the Channel Utilization field 53 indicates the fraction of the time an AP detected its serving channel being busy in the last beacon period. This gives an indication of the traffic load at the AP.
  • STAs upon receiving AP announcement frame 50, STAs could identify the capabilities through the BSSID information field 51 and traffic conditions at different APs through the channel utilization field 53. STAs could also measure the received power for the announcement frames and differentiate between nearby APs and faraway APs. Further, the STAs could maintain a priority list of AP candidates for roaming based on different factors, such as signal strength, traffic load, or a combination of both.
  • a regulatory class 54 is an index into a set of values for radio equipment sets of rules.
  • the regulatory classes specified for 5 GHz operation in the USA are enumerated in Table J.1 of 802.11j, IEEE Standard for Information technology-Telecommunications and information exchange between systems- Local and metropolitan area networks- Specific requirements Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications, Amendment 7: 4.9 GHz-5 GHz Operation in Japan
  • MAC Wireless LAN Medium Access Control
  • PHY Physical Layer
  • the PHY Options field 55 contains the Condensed PHY type and TSF offset Flag below:
  • TSF offset Flag 26 is a one bit field. When it is set to 1 it indicates that a TSF Information field is present.
  • the TSF informationt is 4 octets long and contains TSF Offset and Beacon Interval subfields.
  • Fig. 4 depicts a scenario where STA 26 is currently communicating with AP 61 in first channel.
  • AP 61 transmits information to STA 26 over its serving channel.
  • AP 61 can transmit information corresponding to properties of AP 60 as well as AP 62, and the STA 26 can choose either the AP 60 or AP 62 to start a scan process based on those properties.
  • AP 60 or AP 62 can also transmit in the serving channel of AP 61.
  • STA 26 This enables STA 26 to receive an announcement frame directly from AP 60 or AP 62 without relying on information communicated from AP 61 or from scanning a series of channels contained in a list.
  • AP 60 and AP 62 can transmit an unsolicited AP announcement frame or can wait for STA 26 or another STA to request such a frame. Since STA 26 has access to additional information in a single channel, unlike the prior art, it can chose which AP will provide superior service and switch to that AP without first having to scan through a variety of channels to determine to which AP it should roam. This mitigates the situation where STA 26 would scan a channel associated with an AP that is out of range. For example, in Fig. 4 , STA 26 is moving in the direction of coverage area 621.
  • STA 26 would have to scan a series channels associated with AP 62 and 60. Because STA 26 is not within coverage area 601, STA 26 avoids an unnecessary scan of the channel associated with AP 60. According to the invention, STA 26 simply listens in its operating channel for AP announcement frames. Thus, STA 26 need not scan the channel associated with AP 60 because it will not receive an AP announcement frame from AP 60 in its current operating channel.
  • STA 26 starts moving in the direction of the AP 62 (i.e., from service area 611 corresponding to AP 61 to service area 621 corresponding to AP 62), according to prior art methods, if it tries to connect with the AP 60, it will waste time and energy. This can happen with 50 % of probability if STA 26 scans only the neighbor table sent by the AP 62. With AP announcement frames 50 according to the invention, AP 62 could send periodic advertisements over the serving channel of AP 61. Then STA 26 would be able hear the announcement of the AP 62, and it could use this information to set AP 62 as its best candidate in case of a roaming. In case the STA 26 hears multiple announcements from different APs, it can define the priority based on the signal strength or on the channel utilization.
  • an AP announcement frame 50 can trigger roaming processes not caused by mobility, but for resource-related reasons. For example, when several APs are available in a common area, a STA can start a roaming procedure to a candidate AP that has a lighter load than its current AP. This may be contained in a field of the AP announcement frame 50.
  • Step 501 begins the process.
  • a STA i.e., STA 26
  • an AP x i.e., AP 60
  • the STA checks whether a roaming event was triggered, for example, by a drop in signal strength indicating movement out of range for AP x. If no roaming event was triggered in step 503, STA continues its association with AP x in channel y and returns to step 502. If a roaming event is triggered in step 503, STA checks whether it received an announcement frame from any AP in step 504.
  • STA does not receive an announcement frame, it starts scanning AP candidates to find which AP is the best candidate for roaming according to prior art methods of selection in step 505. If STA does receive an announcement frame in step 504, it updates its Neighboring AP information in step 506. This can include, for example, received power, PHY options, AP capabilities, and channel utilization fields as indicated in update sub-step 506a. Once step 506 is complete, STA updates its AP candidate priorities in step 507. Then, in step 508, STA scans the highest priority AP. There is no deed for STA to switch channels in order to determine which AP is the best candidate for roaming. Additionally, the fact that a frame from a neighboring AP is used helps determine the signal strength whether an AP is reachable.
  • Fig. 6 depicts a flow chart of a process for STAs to use the invention to trigger roaming procedures and perform scanning of AP candidates for roaming.
  • the process in Fig. 6 is an alternative to the roaming trigger events and scanning procedure in Fig. 5 .
  • Step 701 begins the process.
  • STA i.e., STA 26
  • AP x i.e., AP 60
  • STA checks whether it received an announcement frame from any AP. If STA does not receive an announcement frame from an AP, it continues its association with AP x in channel y and returns to step 702. If STA does receive an announcement frame in step 703, it updates neighboring AP information in step 704.
  • STA updates AP candidate priorities in step 705.
  • STA then makes a decision in step 706 whether to start a roaming process. If STA decides not to roam (i.e., based on a preprogrammed protocol) it stays in the same channel with its current AP, as in step 708. If, however, STA decides to begin a roaming process in step 706, it starts scanning the highest priority AP (i.e., based on a prioritization enacted from the neighboring AP information and the AP announcement frame) in step 707.
  • This invention is applicable to any wireless standard in which a mobile station roams from one AP/base station/central controller to another.
  • This invention can be used in any network management solution to support fast roaming between APs and base stations. It can also be used in solutions to support fast roaming between different networks as well, which is called vertical handoff. For instance, roaming between cellular systems and WLAN hot spots, which has been considered an important functionality and a new opportunity for service providers in future wireless networks.
  • This invention is also applicable to some critical applications, such as patient monitoring, in which the wireless devices used to monitor the patients are usually small devices with limited battery life.
  • the roaming process is critical because packet loss and power saving requirements are strict.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Computer Security & Cryptography (AREA)
  • Mobile Radio Communication Systems (AREA)
  • Small-Scale Networks (AREA)

Claims (19)

  1. Verfahren zum Betreiben eines Zugangspunkts (24') in einem drahtlosen Netzwerk, das den folgenden Schritt umfasst:
    Kommunizieren in einem Kanal zum Bedienen von Stationen in diesem Kanal;
    dadurch gekennzeichnet, dass das Verfahren den folgenden Schritt umfasst:
    Übertragen von mindestens einem Ankündigungsrahmen (50) in einem anderen Kanal, in dem ein anderer Zugangspunkt (24) andere Stationen bedienen kann, so dass eine derartige andere Station (26) nach Empfang des mindestens einen Ankündigungsrahmens ermitteln kann, ob der erste genannte Zugangspunkt für das Roaming zur Verfügung steht.
  2. Verfahren nach Anspruch 1, wobei der Schritt des Übertragens von mindestens einem Ankündigungsrahmen (50) das Übertragen von mindestens einem Rahmen mit der Ankündigung von Dienstmöglichkeiten umfasst.
  3. Verfahren nach Anspruch 1, wobei der Schritt des Übertragens von mindestens einem Ankündigungsrahmen (50) das Übertragen von mindestens einem Rahmen mit der Ankündigung der Ressourcen-Verfügbarkeit umfasst.
  4. Verfahren nach Anspruch 1, wobei der Schritt des Übertragens von mindestens einem Ankündigungsrahmen (50) auf Aufforderung von entweder eine Station (26) oder einem anderen Zugangspunkt (24) erfolgt.
  5. Verfahren nach Anspruch 1, wobei der Schritt des Übertragens von mindestens einem Ankündigungsrahmen (50) weiterhin eine unaufgeforderte Übertragung durch den Zugangspunkt (24') umfasst, der das Verfahren ausführt.
  6. Verfahren nach Anspruch 1, wobei der Schritt des Übertragens von mindestens einem Ankündigungsrahmen (50) weiterhin das Übertragen von Messdaten umfasst.
  7. Verfahren nach Anspruch 6, wobei die Messdaten weiterhin mindestens einen Nachbarbericht umfassen.
  8. Verfahren nach Anspruch 6, wobei die Messdaten weiterhin mindestens einen Kanalauslastungsbericht umfassen.
  9. Verfahren nach Anspruch 7, wobei der Nachbarbericht weiterhin mindestens ein Feld bestehend aus empfangener Leistung, PHY-Optionen, Zugangspunkt-Fähigkeiten, Kanalnummer, sowie Kanalnutzungsfelder umfasst.
  10. Computerprogrammprodukt für einen Zugangspunkt (24') in einem drahtlosen Netzwerk, wobei der Zugangspunkt mit einem programmierbare Prozessor (32) ausgestattet ist, wobei das Computerprogrammprodukt einen Anweisungssatz umfasst, der nach dem Laden in den programmierbaren Prozessor den Zugangspunkt in die Lage versetzt, das Verfahren nach Anspruch 1 auszuführen.
  11. Verfahren zum Betreiben einer Station (26) in einem drahtlosen Netzwerk, das die folgenden Schritte umfasst:
    Kommunizieren in einem Kanal mit einem Zugangspunkt (24), der Stationen in diesem Kanal bedient; und
    Initiieren eines Roaming-Vorgangs,
    dadurch gekennzeichnet, dass das Verfahren die folgenden Schritte umfasst:
    Empfangen von mindestens einem Ankündigungsrahmens (50) in dem Kanal, wobei der mindestens eine Ankündigungsrahmen durch einen anderen Zugangspunkt (24'), der andere Stationen in einem anderen Kanal bedient, übertragen wird; und
    Ermitteln der Verfügbarkeit des anderen Zugangspunkt für das Roaming basierend zumindest teilweise auf dem empfangenen mindestens einen Ankündigungsrahmen (50).
  12. Verfahren nach Anspruch 11, wobei der Schritt des Ermittelns weiterhin das Ermitteln der Verfügbarkeit eines Kanals für die Übertragung ausschließlich basierend auf dem mindestens einen Ankündigungsrahmen (50) umfasst.
  13. Verfahren nach Anspruch 11, wobei der Schritt des Ermittelns weiterhin das Aktualisieren von Informationen über benachbarte Zugangspunkte in der Station (26) umfasst.
  14. Computerprogrammprodukt für eine Station (26) in einem drahtlosen Netzwerk, wobei die Station mit einem programmierbaren Prozessor (32) ausgestattet ist, wobei das Computerprogrammprodukt einen Anweisungssatz umfasst, der nach dem Laden in den programmierbaren Prozessor die Station in die Lage versetzt, das Verfahren nach Anspruch 11 auszuführen.
  15. Zugangspunkts (24') für ein drahtloses Netzwerk, mit:
    Mitteln (34) zum Kommunizieren mit einer Station (26) in einem Kanal, um die Station zu bedienen;
    dadurch gekennzeichnet, dass der Zugangspunkt Folgendes umfasst:
    Mittel (32, 34) zum Übertragen von mindestens einem Ankündigungsrahmen (50) in einem anderen Kanal, in dem ein anderer Zugangspunkt (24) andere Stationen bedienen kann, so dass eine derartige andere Station nach Empfang des mindestens einen Ankündigungsrahmens ermitteln kann, ob der erste genannte Zugangspunkt für das Roaming zur Verfügung steht.
  16. Zugangspunkt (24') nach Anspruch 15, wobei die Mittel zum Übertragen (32, 34) vorgesehen sind, um in den Ankündigungsrahmen (50) mindestens ein Bit aufzunehmen, das den Fähigkeiten des Zugangspunktes entspricht.
  17. Station (26) für ein drahtloses Netzwerk mit:
    Mitteln (34), um in einem Kanal mit einem Zugangspunkt (24) zu kommunizieren, der die Station in diesem Kanal bedient; und
    Mitteln (32) zum Initiieren eines Roaming-Vorgangs,
    dadurch gekennzeichnet, dass die Station Folgendes umfasst:
    Mittel (34) zum Empfangen von mindestens einem Ankündigungsrahmen (50) in dem Kanal, wobei der mindestens eine Ankündigungsrahmen durch einen anderen Zugangspunkt (24') übertragen wird, der andere Stationen in einem anderen Kanal bedient; und
    einen Prozessor (32), der vorgesehen ist, um die Verfügbarkeit des anderen Zugangspunkts für das Roaming basierend zumindest teilweise auf dem empfangenen mindestens einen Ankündigungsrahmen (50) zu ermitteln.
  18. Station nach Anspruch 17, wobei der Prozessor vorgesehen ist, um Informationen über benachbarte Zugangspunkte in der Station (26) zu aktualisieren.
  19. Station nach Anspruch 17, wobei die Station (26) Mittel (32) zum Auswählen des anderen Zugangspunktes für die Kommunikation basierend auf der Signalstärke des mindestens einen Ankündigungsrahmens (50) in dem Kanal umfasst, in dem die Station durch den ersten genannten Zugangspunkt bedient wird.
EP06711071A 2005-03-14 2006-03-09 Verfahren und system zur bekanntgabe von zugangspunkt-kandidaten in einem drahtlosen netzwerk Active EP1861957B1 (de)

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US66143405P 2005-03-14 2005-03-14
US75016605P 2005-12-14 2005-12-14
PCT/IB2006/050749 WO2006097874A1 (en) 2005-03-14 2006-03-09 Method and system for signaling available channels in a wireless network

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KR101214124B1 (ko) 2012-12-20
JP4891310B2 (ja) 2012-03-07
EP1861957A1 (de) 2007-12-05
KR20070117586A (ko) 2007-12-12
CN101142788A (zh) 2008-03-12
US9980203B2 (en) 2018-05-22
US20080280621A1 (en) 2008-11-13
ATE468681T1 (de) 2010-06-15
WO2006097874A1 (en) 2006-09-21
DE602006014373D1 (de) 2010-07-01
CN101142788B (zh) 2011-12-21

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